Sahih Bukhari
One-fifth of Booty to the Cause of Allah (Khumus)
Volume: 004 / Book Number: 053 / Hadith Number: 397
Narrated Ibrahim At-Tamimi's father:
'Ali delivered a sermon saying, "We have no book to read except the Book of Allah and what is written in this paper which contains verdicts regarding (retaliation for) wounds, the ages of the camels (given as Zakat or as blood money) and the fact that Medina is a sanctuary in between Air mountain to so-and-so (mountain). So, whoever innovates in it an heresy or commits a sin or gives shelter in it, to such an innovator will incur the Curse of Allah, the angels and all the people, and none of his compulsory or optional good deeds of worship will be accepted. And whoever (freed slave) takes as his master (i.e. befriends) other than his real masters will incur the same (Curse). And the asylum granted by any Muslim is to be secured by all the other Muslims, and whoever betrays a Muslim in this respect will incur the same (Curse)."